This union has a nut that fits on pumps with a male thread measuring 62 mm outside diameter (this type of thread is known as 1.5" MBT), and connects to 50 mm pipe.
If the nut breaks, you can replace it with a two-part nut that is screwed together, and therefore perfect for repairs when you need to avoid cutting pipe.
Inside diameter of the thread on the tightening ring: 59.5 mm
Outside diameter of the corresponding male thread on the pump: 62 mm
Fits 1.5" pipe (inside diameter: 50 mm)